hot deserts revision september

hamada

bare, rocky surfaces

reg

stony deserts with rock fragments over large plains

erg

mainly sand ‘sand sea’

arid areas classification (+characteristics)

receives less than 250mm of rainfall annually

* very dry climates
* low levels of precipitation, high rates of evapotranspiration
* high diurnal temperature ranges due to lack of cloud cover

distribution of arid areas

generally located between the tropics, 15-30 degrees North and South of the equator

* they are found in areas of high pressure (which is between the tropics due to global atmospheric circulation)

climate characteristics

* less than 250mm of rainfall annually
* have a high diurnal temperature range: during the day there are high levels of insolation as solar radiation is not reduced by cloud cover, during the night clear skies allow ground temperatures to fall rapidly
* can be as high as 37 degree diurnal temperature ranges
* the highest temperature ever recorded was 56.7 degrees in Death Valley, California 1913

soil characterises

* thin, highly saline and lack organic content
* capillary action draws water and minerals from the water table to higher levels of soil, when the water evaporates only salt is left behind
* there is not enough water to support plants and animals so there is a lack of organic content
* small surface particles have low water retention

vegetation characteristics

* have thick waxy cuticles and small, spiky leaves to prevent moisture loss
* fleshy stems and bulbous roots increase ability to store moisture
* deep and wide root systems increase water gathering ability
* flowering quickly forms a short life cycle to follow erratic storms
* fleshy stems, bulbous roots and thick protective bark increase salt tolerance
* adapted to deserts: xerophytes e.g. cacti and giant agave can grow in deserts

water balance in hot deserts

* there are high temperatures and dry air leading to high evapotranspiration
* this means there is little storage and runoff
* plants and animals must adapt to the scarcity of water

aridity index

\
the relationship between precipitation and potential evapotranspiration

* aridity index = annual precipitation/annual potential evapotranspiration
* for arid areas this is between 0.05 and 0.2